1. Field of the Invention
The present invention relates to an ink-jet printing machine and a printing method in which a plurality of inks are ejected from ink-jet heads in order on a printing sheet transferred along a transfer path.
2. Description of the Related Art
A printing machine disclosed in Japanese Patent Laid-Open Publication No. 2004-276486 shows a printing method in which color inks are ejected on a printing sheet from ink-jet heads aligned along a transfer path formed by a transfer belt. The printing machine transfers the printing sheet fed by a sheet feeding part, performs printing during the transfer, and discharges the printed sheet from a sheet discharging part. With increased demand for high-speed printing, this printing machine is equipped with a transfer belt that performs a high-speed transfer.
Printing sheets often get deformed because of wetness or dryness due to humidity changes. FIG. 1 shows such a printing sheet 2002 with wrinkles 2021 on the edge. As shown in FIG. 2B, when the printing sheet 2002 is transferred into the ink-jet printing machine by a transfer belt 2106a, a deformed portion of the printing sheet 2002 leaves from the upper surface of the transfer belt 2106a and hence contacts with an ink-jet head 2104. This contact causes damage to the ink-jet heads or leads to blocking of ink ejection.
In order to detect the deformation of the printing sheet, Japanese Patent Laid-Open Publication No. H08-198477 shows a printing machine having an optical sensor.
In order to minimize the leaving of the printing sheet under the ink-jet head, a conventional printing machine has a guide roller provided upstream of the ink-jet head or a steel plate 2053 covering the transfer path to keep pressing the deformation as shown in FIG. 3.